Warm drinking water conduit system

ABSTRACT

The invention relates to a warm drinking water conduit system, with at least one drinking water heater/storage tank for warm drinking water, with a fresh water supply conduit for supplying cold drinking water into the tank and with a heat exchanger connected to a heating circuit and intended for heating the supplied cold drinking water in the tank to a predetermined temperature and for maintaining the warm drinking water temperature in a conduit system connected to the tank and having tapping points for the extraction of warm drinking water, the warm drinking water circulating in the conduit system by means of a pumping device, wherein the drinking water heater/storage tank is tied into the warm drinking water circulation circuit, the circulation temperature in the entire conduit system being maintained at a level such that the warm drinking water is largely free of microorganisms, in particular legionellae, and that the tank is thermally disinfected of microorganisms in rota in a largely reduced conduit branch during a relatively short time span by means of an increased circulation temperature.

[0001] The invention relates to a warm drinking water conduit systemaccording to the preamble of claim 1.

[0002] There are known drinking water conduit systems which havehitherto not sufficiently ensured that, above all, microorganismsharmful to health, in particular legionellae, do not multiply in warmdrinking water. This applies mainly to relatively large conduit systemswith central drinking water heater/store, where there may be stagnantwater with temperatures of between 30° C. and 45° C.

[0003] When water contaminated in this way with legionellae is extractedfrom the conduit system, for example, by showers, whirlpools orair-conditioning systems in which breathable aerosols are formed, thereis known to be a considerable risk of influenza-like illnesses andpneumonia.

[0004] It is known that legionellae are killed above 50° C. and that thekilling time decreases with an increase in temperature.

[0005] The object of the invention, therefore, is to design a warmdrinking water system of the above type, in such a way that, when warmdrinking water is extracted, the risk of illness caused bymicroorganisms, in particular legionellae, can be largely ruled out. Atthe same time, thermal disinfection is to be capable of beingimplemented by means which are simple in terms of hydraulics andregulation and are easy to operate, while the investment costs can bekept comparatively low under energy-optimized conditions. In thiscontext, the idea on which the invention is based is to keep thedrinking water heater/storage tank constantly tied into the warm watercirculation circuit, the circulation temperature being maintained at alevel such that the warm drinking water in the warm water conduit systemcan be kept largely free of microbacteria, in particular legionellae,and such that the tank can be thermally disinfected by rota, during arelatively short time span, in a substantially reduced conduit branch bymeans of an increased circulation temperature.

[0006] The object is achieved, according to the invention, by means ofthe defining features of claim 1. Advantageous embodiments may begathered from the features of the subclaims and from the followingdescription.

[0007] The invention is described below, merely for one exemplaryembodiment, by means of a diagrammatic drawing. The drawing containsonly those parts which are necessary for understanding the invention.

[0008] The exemplary embodiment according to the invention shows acentral drinking water heater/storage tank 1 with a known inner heatexchanger 2 which is connected to any desired heating source 6 via aheating circuit 3 with a heating forward flow 4 and with a heatingreturn flow 5. The tank 1, for example having a capacity of >400 liters,may be installed, together with the heating source 6, in a basement orin another suitable place of installation. In the forward flow 4 theheating circuit 3, there are, in series, a shutoff valve 7, a 3-waymixing valve 8, a pump 9, a nonreturn device 10, a temperature sensor 11and a further shutoff valve 12. A further shutoff valve 13, a furthertemperature sensor 14 and yet a further shutoff valve 15 are arranged inthe return 5, depicted by dashes, of the heating circuit 3. By means ofthe three-way mixing valve, the temperature of the forward flow 4 can beregulated via an admixing conduit 16, likewise depicted by dashes, tothe return 5.

[0009] The functioning of the heat exchanger 2 in conjunction with theheating circuit 3 is clear to any person skilled in the art and does notneed to be explained in any more detail. The heating circuit 3 may beconnected to a district heat generator or other heat transfer mediainstead of to the heating source 6.

[0010] The heat exchanger 2 is arranged, here, within the tank 1. It isclear that a heat exchanger may also be arranged outside the tank 1 andin contact with the tank inner wall, so that heat is not transmitteddirectly to the drinking water in the tank, but is transmitted to thedrinking water via the tank inner wall. The tank 1 is then designed in aknown way as a double-jacket boiler.

[0011] The tank 1 is connected via an outlet conduit 17 to a warmdrinking water conduit system 18 (shown in simplified form here), fromwhich any desired number of tapping points, even on different floors ofa building, can be branched off.

[0012] In the example, merely for the sake of simplicity, and withoutany restriction, only on the first floor of a building, a warm drinkingwater tapping point 19 is connected via a warm water meter 20 and ashutoff valve 21 to the warm drinking water conduit system 18, which,with the tank 1 tied in, forms a closed circulation circuit in thedirection of the arrows 23, for which purpose the warm water conduitsystem 18 is connected to the tank 1 via a branch 18′ upstream of theshutoff valve 21 and via a return conduit 22. For the circulation ofheated drinking water in the conduit system 18, the return conduit 22has connected into it a pump 24 which sucks in warm water from theconduit system 18 and feeds it back into the tank 1 via the returnconduit 22.

[0013] The heat exchanger 2 is designed in such a way that, duringnormal operation, the tank 1 discharges warm water with a temperature ofabout 60° C. into the conduit system 18 via the outlet conduit 17. Bymeans of temperature sensors, not shown, and temperature regulation, itis possible in a known way to ensure that the warm drinking watercirculating in the conduit system 18 cools at most by 5K and thetemperature in the return line 22 to the tank 1 is still at least at 55°C. The return conduit 22 is connected via a connection 25, in the middleregion of the tank 1 just above the heat exchanger 22, to the tank 1,which is connected in the conventional way to a cold drinking waterconduit 28 via a first shutoff valve 26, a nonreturn valve 26′, a watermeter 27 of the second shutoff valve 26″. The connection 29 of the coldwater conduit 28 to the tank 1 is located in the lower region of thelatter. In this case, the cold drinking water line 28 is previously ledto a level above the highest point of the tank 1, where a safety valve30 is arranged. The conduit 28 has branching off from it a conduit 28′,to which any desired number of tapping points are connected. In theexample, only one cold drinking water tapping point 19′ is connected inparallel with the warm drinking water tapping point 19 via a shutoffvalve 21′.

[0014] A three-way changeover valve 31, which precedes the pump in thedirection of flow of the warm water 24, is connected into the returnconduit 22.

[0015] The three-way changeover valve, in one of its switchingpositions, is switched to passage to the tank 1. In its other position,it bypasses the outlet conduit 17 via a branch conduit 32 to the returnconduit 22.

[0016] Consequently, when the three-way changeover valve is in thepassage switching position, with the tank 1 being tied in, the warmdrinking water circulates in the entire conduit system 18, together withthe tapping points branching off from it (in the example, only thetapping point 19). This circulation (large circuit) is designated, here,as “full circulation” and largely ensures that the entire conduit system18 is free from legionellae.

[0017] If the three-way changeover valve is in the bypass position, withthe tank tied in, the warm drinking water circulates only in the conduitcircuit which is substantially reduced via the branch conduit 32 and islocated near the tank 1 (small circuit). This circulation is designated,here, as a bypassed circulation circuit or “bypass circulation”. Thereduced conduit length of the small circuit may amount to only a fewmeters, for example 2 to 3 m, in the immediate vicinity of the tank 1.

[0018] The bypassed circuit remains constantly connected to theremaining conduit system 18, warm drinking water circulating only in thebypassed circulation circuit and not also in the rest of the connectedconduit system.

[0019] In the return conduit 22, the pump 24 is followed in thedirection of flow by a nonreturn device 33, and, upstream of theconnection 25 for the return line 22 to the tank 1, a conduit 34branches off which is lead to a connection 35 to the bottom of the tank.

[0020] A first balancing valve 36 for the fixed setting of a first partstream if located in the branch conduit 34, and a second balancing valve38 for the fixed setting of the remaining part stream is located in thereturn conduit 22 between the connection 25 of the latter to the tank 1and branch 37 to the conduit 36.

[0021] For a predominant time of the day, the three-way changeover valveis switched to passage, so that the warm drinking water flows in theentire conduit system at a minimum temperature of about 55° C. in thereturn conduit. Full circulation may be selected, for example, for 23 h,except, for example, in the night between 2 and 3 o'clock, when,according to experience, warm drinking water is extracted only rarely bythe users.

[0022] In the relatively short time span of, for example, 50 to 60minutes, preferably in the night between 2 and 3 o'clock, the warmdrinking water is rapidly increased to about 65° C. by means of the heatexchanger 2 via temperature regulation, not shown, so that reliablethermal disinfection of the tank 1 and of the conduits in the region ofthe bypass circulation (small circuit) can be carried out during thistime span.

[0023] In order, in this case, to ensure that all the warm water layersof the tank assume a temperature of 65° C., at which legionellae arerapidly killed, the two balancing valves 36 and 38 are set fixedly insuch a way that a relatively small part stream of selected size as thewarm drinking water sucked in by the pump 24 is introduced into the tankfrom below via the branch conduit 34, the part stream supplied flushingthrough the water at the bottom and below the heat exchanger 2 andbetween the tubes of the heat exchanger. In order at the same time toprevent the water from swirling in the tank, the part stream supplied tothe tank bottom preferably amounts to about 10% of the volume sucked inby the pump 24.

[0024] As a result, even relatively colder warm water zones within thetank 1 are brought to about 60° C. during full circulation (largecircuit) and to about 65° C. during bypass circulation (small circuit),in order to destroy preferred breeding places of the legionellae.

[0025] The time span of 50 to 60 minutes at a temperature of 65° C., forexample in the night between 2 and 3 o'clock, is fully sufficient tokill all the legionellae in the tank with a high degree of reliability.

[0026] The branched-off part stream, lead via the conduit 34 to the tankbottom, of, for example, about 10% of the total volume sucked in by thepump 24 can be set via the valves 36 and 38, for example, in such a waythat it is cut in only during bypass circulation, not also during fullcirculation. However, the valves 36 and 38 may also switched in such away that the, for example, 10% part stream is cut in both during fullcirculation and during bypass circulation, that is to say constantly, orelse only during full circulation. The part stream quantity may becapable of being set selectively. An approximately 10% part stream hasproved particularly appropriate. It is clear that the invention is notrestricted to this.

[0027] Bypass circulation over a total conduit length of a few meters,for example 2 to 3 m, ensures thermal disinfection, in particular oflegionellae, with minimum energy consumption. It is also ensured thatthe use of warm drinking water continues to be possible at all theexisting tapping points during thermal disinfection. Since, as stated,bypass circulation takes place only in a relatively short time span of,for example, 50 to 60 minutes, when the conduit system is frequentedparticularly rarely, it is justifiable for there to be the disadvantagethat, when warm drinking water is extracted during this time span, thetemperature of the stagnant water outside bypass circulation may becooled to slightly below 55° C. and therefore the cooled water first hasto be extracted before water at the temperature increased to 65° C. canbe branched off from bypass circulation. There is no risk of theformation of legionellae during this short time span of, for example, 50to 60 minutes. Subsequent full circulation at at least 55° C. to 60° C.over 23 hours is fully sufficient to keep the entire conduit system,including the tank, free of legionellae, in such a way that a growth oflegionellae during bypass circulation can be largely ruled out.

[0028] The regulation of temperature to 60° C. and to 55° C. can takeplace centrally in the conventional way, known temperature sensors andthe temperatures monitors being arranged at suitable points in the tankand in the conduit system. Thus, the branch 37 in the return conduit 22may be preceded by a temperature sensor 39 which monitors the warm watertemperature in the return conduit briefly, for example at minuteintervals.

[0029] Time control for changing over the temperature in rota from 60°C. to 65° C. and back to 60° C. during specific day times and nighttimes and for reversing the valves in rota for full circulation andbypass circulation may likewise be carried out from a central controlapparatus.

[0030] It is clear to the person skilled in the art that, in arelatively large drinking water conduit system according to theinvention, a plurality of drinking water heater/storage tanks may beconnected in parallel to a drinking water conduit 28, each tank 1 beingprovided with a heat exchanger 2, said heat exchangers being capable ofbeing connected in parallel to their own heating circuit 3, and bypasscirculation including both tanks, and there being connected to thebottom of each tank in each case a conduit 34, via which parallel partstreams are branched off from the bypass circulation circuit common toboth tanks, so that complete thermal disinfection of both tanks can beensured.

1. A warm drinking water conduit system, with at least one drinkingwater heater/storage tank for warm drinking water, with a fresh watersupply conduit for supplying cold drinking water into the tank and witha heat exchanger connected to a heating circuit and intended for heatingthe supplied cold drinking water in the tank to a predeterminedtemperature and for maintaining the warm drinking water temperature in awarm drinking water conduit system connected to the tank and havingtapping points for the extraction of warm drinking water, the warmdrinking water circulating in the conduit system by means of a pumpingdevice, wherein the drinking water heater/storage tank is tied into thewarm drinking water circulation circuit, first control means beingpresent, which maintain the circulation temperature in the entireconduit system at a value such that the warm drinking water is largelyfree of microorganisms, in particular legionaellae, and second controlmeans being present, which, in a largely reduced conduit branch, monitorthe thermal disinfection of the tank and of the reduced circuit in rotaduring a relatively short time span by means of an increased circulationtemperature.
 2. The warm drinking water system as claimed in claim 1,wherein a) the conduit system is connected to an outlet conduit (17) ofthe tank (1) for the extraction of warm drinking water from differenttapping points (19) and to a return conduit (22) to the tank (1) for thereturn of the warm drinking water not extracted, b) connected into thereturn conduit (22) is a three-way changeover valve (31) which in rota,in one of its two positions, ensures circulation in the entire conduitsystem, including the tank (1), during the longer time span (long-termfull circulation) and, in its other position, by the connection of abypass conduit (32) between the outlet conduit (17) and the returnconduit (22) in the vicinity of the tank (1), ensures circulation in thelargely reduced conduit system, including the tank (1), during acomparatively short time span for the thermal disinfection of the tank(bypass circulation), the connection to the remaining conduit system inwhich the warm drinking water does not circulate remaining open, c) avalve control is present, which, according to a selected time program,monitors the in-rota changeover of the three-way changeover valve (31)from its normal position for full circulation into the relativelyshort-term special position for bypass circulation, and back, and d)there is temperature regulation which is monitored by a temperaturesensor (39) and which, during the longer time span of full circulation,keeps the warm water temperature in rota at a first temperature valuewhich largely rules out infection with microbacteria, in particularlegionellae, and which, during the comparatively short time span ofbypass circulation, keeps the warm water temperature in rota at anincreased second temperature value for the thermal disinfection of thetank (1).
 3. The drinking water conduit system as claimed in claim 2,wherein the temperature regulating value for the time span of fullcirculation is about 60°, below which said value does not fall by 5K,and wherein the increased temperature regulating value for the bypasscirculation is about 65° C.
 4. The drinking water conduit system asclaimed in claims 2 and 3, wherein bypass circulation is selected once aday during a time span of about 50 to 60 minutes minimally frequented bythe user and full circulation is selected daily during the remainingtime span.
 5. The drinking water conduit system as claimed in claims 2and 4, wherein the tank (1) is a continuous-flow drinking water heaterwith warm drinking water stored capacity of >400 l, and wherein the heatexchanger is arranged in the tank or within a double wall of the tank(3).
 6. The drinking water conduit system as claimed in one of claims 1to 4, wherein the pump (24) for full and bypass circulation follows thethree-way changeover (31) valve in return conduit (22) in the directionof flow.
 7. The drinking water conduit system as claimed in one ofpreceding claims 1 to 5, wherein the conduit length for bypasscirculation is a few meters long.
 8. The drinking water conduit systemas claimed in one or more of the preceding claims, wherein the returnconduit (22) is connected to the tank (1) in the middle region of thelatter, wherein a conduit (34) connected to the tank bottom branches offfrom the return conduit (22) downstream of the three-way changeovervalve (31) and pump (24) and of the connection point (25) to the tank(1) in the direction of flow, wherein a first balancing valve (36) isarranged in the branch conduit (34) and a second balancing valve (38) isarranged in the return conduit (22) between the branch point (37) andthe connection point (25) to the tank (1), and wherein a valve controlis present, which ensures that, during full circulation and bypasscirculation or only during full circulation or only during bypasscirculation, in each case only predetermined part streams of the warmdrinking water flow via the two balancing valves (36 and 38), on the onehand, to the tank bottom and, on the other hand, to the middle part ofthe tank.
 9. The drinking water conduit system as claimed in claim 8,wherein the fixedly set part stream led to the tank bottom amounts toabout 10% and the fixedly set remaining part stream led to the middlepart of the tank 1 to about 90% of the warm drinking water sucked in bythe pump 24 in the return conduit (22).